The subject matter disclosed herein relates to coated belts or ropes used, for example, in elevator systems. More specifically, the subject disclosure relates to wear detection (e.g. of corrosion, fretting, etc.) of coated belts or ropes used for elevator suspension and/or driving.
Elevator systems utilize ropes or belts operably connected to an elevator car, and routed over one or more sheaves, also known as pulleys, to propel the elevator car along a hoistway. Coated steel belts in particular include a plurality of wires located at least partially within a jacket material. The plurality of wires is often arranged into one or more strands and the strands are then arranged into one or more cords. In an exemplary belt construction, a plurality of cords is typically arranged equally spaced within a jacket in a longitudinal direction.
During normal elevator operation, coated steel belts are subjected to a large number of bending cycles as the belt travels over drive sheaves and deflector sheaves of the elevator system. These bending cycles cause a degradation of the breaking strength of the wires or cords within the coated steel belt via the mechanism of wire fretting or fatigue. Such fatigue is a major contributor to reduction in service life of the coated steel belt. While the service life of the coated steel belt can be estimated through calculation, a more accurate estimation of remaining life of the coated steel belt is often obtained by utilizing a life-monitoring system.
One such system is called resistance-based inspection (RBI). An RBI system is secured to the belt at a fixed point of the elevator system and monitors an electrical resistance of each cord in the belt. Since the electrical resistance of each cord is proportional to its cross-sectional area, changes is electrical resistance can be correlated to reduction in cross-sectional area of the cord, indicating an amount of fretting of the cord, and a corresponding remaining service life. Some cord configurations, however, do not exhibit a significant, measurable change in resistance which can be correlated to a number of bending cycles or cord degradation. In such cases, assessment of belt condition based upon changes in electrical resistance of the cords is difficult due to the small magnitude of change in electrical resistance of the cords as the cords wear.